linux-kernel - Re: [PATCH mm-unstable v2 1/3] mm/contig_alloc: support __GFP

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Message-ID: <ZseGjKXaZIvgu9vQ@casper.infradead.org>
Date: Thu, 22 Aug 2024 19:42:20 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Yu Zhao <yuzhao@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>, Zi Yan <ziy@...dia.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH mm-unstable v2 1/3] mm/contig_alloc: support __GFP_COMP

On Thu, Aug 22, 2024 at 11:23:04AM -0600, Yu Zhao wrote:
> Andrew, could you patch up the line above? This is what it's supposed
> to check:
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 59266df56aeb..03ba9563c6db 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -452,7 +452,7 @@ static inline struct folio *folio_alloc_gigantic_noprof(int order, gfp_t gfp,
>  {
>  	struct page *page;
>  
> -	if (WARN_ON(!order || !(gfp | __GFP_COMP)))
> +	if (WARN_ON(!order || !(gfp & __GFP_COMP)))
>  		return NULL;

I don't think we should do this at all.  Just this should be enough:

	gfp |= __GFP_COMP;

same as folio_alloc() (or now folio_alloc_noprof()).
Do we really caree if somebody tries to allocate a gigantic page with an
order of 0?  It's weird, but would work, so I don't see the need for the
warning.

>  	page = alloc_contig_pages_noprof(1 << order, gfp, nid, node);
>